Thin film processing is used in many industrial applications, such as semiconductor fabrication, optical component fabrication, and micro-electro-mechanical systems ("MEMS"). In many, if not most, applications, a thin film layer is formed on a major surface of a substrate, such as the polished surface of a silicon wafer or the surface of a glass blank. However, some devices and fabrication process need to deposit a thin film on a surface that is vertical to the major surface of the substrate. For example, a structure of a MEMS device might be formed by deep reactive ion etching ("DRIE"), and it might be desirable to deposit a layer on a vertical surface or surfaces. Unfortunately, most deposition processes are not suited for forming such a layer. In particular, conventional processes tend to build up material proximate to the major surface while not depositing as much material distal from the major surface. This can cause a rough or uneven surface, affecting the performance of the deposited layer.
Thus it is desirable to provide a method and apparatus for forming an even layer of thin film material on a vertical surface of a structure formed on a substrate.